Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $94.74   12.268%   $106.3627   $106.36   $106.35   $106.40  
  Purchase #2 $60.65   10.462%   $66.9952   $67.00   $67.00   $67.00  
  Purchase #3 $173.59   11.735%   $193.9608   $193.96   $193.95   $194.00  
  Purchase #4 $34.41   7.729%   $37.0695   $37.07   $37.05   $37.10  
  Purchase #5 $28.53   4.238%   $29.7391   $29.74   $29.75   $29.70  
  Purchase #6 $161.48   12.415%   $181.5277   $181.53   $181.55   $181.50  
  Purchase #7 $152.89   13.271%   $173.18   $173.18   $173.20   $173.20  
  7 purchase totals = $706.29       $788.8350   $788.84   $788.85   $788.90